Sisyphean
/ˌsɪsɪˈfiːən/
Definition 1 of 1
Pro Tip 1/3Greek Mythology
Originates from Greek myth where Sisyphus eternally rolls a boulder uphill. Implies futile effort. 
His attempt to please everyone felt like a sisyphean ordeal.
Pro Tip 2/3Literary Tone
Often used in a literary or intellectual context to evoke a sense of struggle against the impossible. 
Writing her novel was a sisyphean endeavor, filled with constant revisions.
Pro Tip 3/3Never-Ending Struggle
Indicates a task is not just difficult, but also lacks a clear endpoint or solution. 
Campaigning for peace can sometimes seem like a sisyphean venture.